In the conventional seaming process for seaming the end member of a container to the body member of the container, the edges of the two members are rolled into a seam to form a plurality of layers of material disposed radially outwardly at the end of the container. The seaming apparatus includes one or ore appropriately profiled forming wheels for applying an inwardly directed radial force on the edge portions of the container end and body members as the container is rotated about a fixed axis. The radial force exerted by the forming wheel or wheels during the rolling of the seam is resisted by an internal support. In a conventional seaming apparatus, this internal support is comprised of a seaming chuck having an outer ring attached to a cylindrical central body. The ring is formed with a smooth cylindrical edge surface where it has to withstand the force exerted by the forming wheel or wheels. Beneath this surface, the seaming chuck has a frustoconical portion designed to facilitate the penetration of the seaming chuck into the container end which is generally preformed as a stamped cup shaped member.
The side surface of the container end member bears against the smooth cylindrical wall of the chuck; and as the container end and body members are rotated by the seaming chuck, the force exerted by the opposed forming wheel or wheels, rolls the edges of these members into the seam.
In order to effect a proper seam in conformity with professional standards, it is necessary that the seam provide a uniformly sealed joint about the entire periphery of the container. Present seaming apparatus is not completely satisfactory in this regard, especially where the seam is rolled into a large number of layers of material as with a seam having five or more layers of material. Also, where there are variances in the thickness of the material from which the container end and body members are formed, difficulties in rolling a satisfactory seam have resulted. This is particularly evident where the nominal thickness of the material, typically sheet metal, is substantial and the thickness tolerances produce greater variations in total thickness throughout the sheet metal than would occur if very thin material were used.
In forming an acceptable rolled seam, it is necessary that the layers of material defining this seam be closely compressed against each other around the entire periphery of the container. In order to do this, the seaming apparatus is constructed so that the forming wheel and seaming chuck are radially spaced from each other during the final rolling of the seam by a distance which is generally equal to the nominal thickness of the sheet metal multiplied by the number of layers of material which will be formed at the seam structure. With a triple seam, for example, this spacing will be equal to the thickness of the sheet metal multiplied by seven, five layers of material forming the main body portion of the seam and two layers forming the sides of the container end and body members against which the seam is formed.
If the thickness of the sheet metal were perfectly uniform, a proper seaming would be assured. However, where there are variations in thickness resulting, for example, from the manufacturing tolerances used in the production of the sheet metal, these variations exist and are magnified by the number of layers of material formed at the seam. Of particular significance is the condition where the thickness of the sheet metal is greater than the nominal thickness whereby excess material results at the seam.
With conventional seaming apparatus, thickness variations will tend to produce an improper seam, either one where the sealing effect of the seam is not uniform about the entire periphery of the container or one where excess material has been caused to undergo a cold rolling by being squeezed between the forming wheel and chuck thereby weakening the seam. In some circumstances both conditions may be produced.
In addition to the above problems as caused by thickness variations, conventional seaming chucks have a smooth peripheral edge surface engaging the side surface of the container end member. Such constructions will tend to cause the container end member to slip relative to the edge surface of the chuck. The effects of this slipping on the seaming process are well known to those skilled in the art.
The quality of the rolled seam is closely associated with the regular rotation of the container end member engaged on the seaming chuck, which is directly dependent upon the manner in which the container body and end members are rotated. Moreover, in the case of sheet metal with a protective coating (a preliminary layer of paint, for example), any slip of the container end member on the seaming chuck causes local damage as a result of this protective coating being worn away.
To avoid the slippage problem, seaming chucks have been constructed with knurled or serrated surfaces for engaging against the container end member. Typical constructions are disclosed in U.S. Pat. Nos. 2,181,237, 2,511,738 andd 3,734,043. Although these constructions do provide for a non-slipping type of engagement, they tend to mar or damage the surface of the container end member due to their rough surface. And, as will be appreciated, this can be a serious problem with coated materials.
Seaming chucks have also been constructed with indentations or protuberances on their container engaging surface. Typical constructions are disclosed in U.S. Pat. No. 2,906,430 and 3,221,922 and British Pat. No. 1,220,129. To the extent that these constructions tend to prevent slippage, they do not combine this into a chuck configuration which will also accommodate thickness variations in the container material so as to prevent uneven sealing as well as cold rolling of the material. Generally, this is so because these prior constructions were designed for use in manufacturing thin walled cans where problems of thickness variation are not significant.